The East Coast Whale Die-Offs: Unraveling the Causes
In early December of 2016, the carcasses of juvenile humpback whales began turning up in the busy waters around the mouth of Virginia’s Chesapeake Bay. By the end of February, 10 animals had been found within about a 200-mile stretch of coast between Virginia and North Carolina.
Though scientists did not yet know it, the spate of deaths marked the start of an “unusual mortality event” (UME) for humpback whales. Such episodes, which are codified in the Marine Mammal Protection Act, involve unexpected strandings and a “significant die-off” of any marine mammal population. (A “stranding” can describe both a live or a deceased animal.)
After a decline in strandings in 2021, a dramatic spike appears to once again be underway. Between December 1, 2022 and March 1, 2023, 16 humpbacks have stranded on or near shorelines from North Carolina to New York, the highest number ever recorded during that particular three-month period. Ten of the whales have been found on beaches in, or just offshore from, New Jersey and New York. (Other whale species, including four critically endangered North Atlantic right whales, have also stranded along the U.S. East Coast since January.)
Scientists who study whale behavior say it is impossible to definitively link the strandings to a single cause.
This winter’s humpback strandings in New York and New Jersey look strikingly similar to those that occurred from December 2016 through February 2017 in Virginia and North Carolina, in terms of number of animals, geographic radius, and average number of days between strandings. And yet activist groups, politicians, and the media are falsely framing the New York and New Jersey strandings as unprecedented. The claim was first made in January, after the states experienced five humpback strandings, and the allegation has since engulfed coastal towns in New Jersey, where construction of the largest offshore wind farm in the U.S. is set to begin as early as next year.
Building wind farms off the Eastern Seaboard has been discussed for decades. However, the Biden Administration, with the support of 11 coastal states, has moved quickly to carve out huge swaths of ocean for development. New Jersey has been the most ambitious, setting a goal to power more than 3.2 million homes with offshore wind energy by 2035. Last year, the energy companies Ørsted and Atlantic Shores began conducting seafloor surveys off the coast of southern New Jersey for their respective lease areas, which have space for hundreds of turbines.
That work drew little attention. But after the January strandings, groups opposed to offshore wind development began blaming the deaths on the surveying, some of which uses pulses of sound to map the seafloor surface and subsurface. Since then, 30 mayors of coastal New Jersey municipalities, along with several of the region’s state and federal representatives, have called on both New Jersey’s governor and President Biden to pause all activity by offshore wind companies until an investigation determines the cause of the strandings.
“The work related to offshore wind projects is the primary difference in our waters,” New Jersey state senator Vince Polistina said in January, referring to recent changes in the ocean that might be drastic enough to trigger whale strandings. “And it’s hard to believe that the death of [these] whales on our beaches is just a coincidence.”
However, the Marine Mammal Commission, an independent government agency that oversees the conservation of marine mammals and their environment, said in February that “there is no evidence to link these strandings to offshore wind energy development.” It added, “Although these strandings have generated media interest and public scrutiny, this is not an unusually large number of whales to strand during winter.” Indeed, since the National Oceanic and Atmospheric Administration (NOAA) declared the start of the UME in 2016, both New Jersey and New York have seen high numbers of strandings — New York alone has had 36 in the past seven years — though they have occurred more often in the spring and summer.
While certain types of sound have been shown to harm cetaceans, the scientists who study the impact of sound on marine mammals say the types recently used by Ørsted and Atlantic Shores operate at frequencies that pose little risk to baleen whales like the humpback. And, scientists who study whale behavior in general say it is impossible to definitively link the strandings to a single cause given the complexity of the ocean, the dramatic changes the North Atlantic has experienced in recent decades, and how much is still unknown about how these changes might be affecting baleen whales.
Warming in the Gulf of Maine, a key feeding ground for humpbacks, may be influencing shifts in whale migration.
“If we’re being honest here, this isn’t just about humpback whales,” says Alex Costidis, who leads the Virginia Aquarium & Marine Science Center’s Stranding Response Program and is also a member of the National Marine Fisheries Service’s working group for Marine Mammal Unusual Mortality Events. “This is about a pretty stressed marine environment that we are continuing to stress at increasing rates, while really having a very poor understanding of what the ultimate impacts are.”
Because there are no large-scale wind farms off the U.S. East Coast, the only way to achieve the best possible understanding of their impacts on marine life, Costidis and other scientists say, is to have a better understanding of the marine environment now — not after turbines have been constructed. Indeed, last year the state of New Jersey mandated Ørsted and Atlantic Shores to dedicate $26 million to baseline research, like using seafloor-anchored listening devices to monitor marine mammal presence and analyzing environmental DNA to track the movements of fish species. Some of that work has started. Some will begin this year. Already, though, there are clear signs of the stressors to the marine environment that worry Costidis.
The North Atlantic has warmed dramatically in recent decades. In 2022, its “ocean heat content” — a measure of the amount of heat stored by the ocean — reached its highest point since record-keeping began in the 1950s. The Gulf of Maine, a key feeding ground for humpback and other baleen whales, is warming even faster. This may be influencing seasonal changes in the whales’ distributions that scientists have noticed in the last few decades — changes that mirror those that are occurring among their prey, which include krill and Atlantic menhanden.
Historically, humpbacks largely remained in northern waters between the Gulf of Maine and Norway from spring through summer, then migrated south to the tropics to calve and mate in the winter. But recently, their distribution has been wider. “What we’ve seen in the past two decades is humpback whales in different areas to the south, most of them seeming to be juveniles, feeding off the Mid-Atlantic states in winter when most of the population would be migrating to the Caribbean,” says Jooke Robbins, a senior scientist with the Center for Coastal Studies’ Humpback Whale Studies Program. “In the past decade, we’ve started to see whales popping up in summer in the waters off New York, New Jersey, and Rhode Island, which seems to be an extension of the normal feeding season.”
Kevin Wark, a commercial fisherman who has spent his life and career working the waters off New Jersey, also says that predator-prey dynamics in the New York Bight — as the waters off New York and New Jersey are known — have shifted significantly in recent years. “The menhaden population is strong and the whales have learned that they’re an easy target,” says Wark, who has worked as Atlantic Shores’ “fisheries liaison officer” since 2019. Recalling the past year, he continues, “I’ve never seen so many humpbacks in the ocean — just crazy amounts of whales.”
Over the past decade, the volume of goods handled by ports up and down the coast — but especially in New Jersey, New York, Pennsylvania, and Delaware — has grown rapidly. During the coronavirus pandemic, shipping traffic exploded. The number of containers handled at the Port of New York and New Jersey increased by 27 percent between 2019 and 2022. Just to the south, the Port of Philadelphia is now the fastest growing port in the nation.
Almost all the humpback strandings that occurred in New York and New Jersey this winter had clear signs of a vessel strike.
This confluence of more whales and more ships in a new area presents an unfortunate but logical clue to the UME. Researchers conducted partial or full necropsies on about half of the stranded whales since the UME began in 2016, and about 40 percent of those examined had signs of injury at the hands of humans. “We continue to see evidence suggesting similar causes at play, namely vessel collisions and fishing gear entanglement,” Costidis says. “We can speculate all we want, but that’s what the evidence is currently showing us.”
Indeed, almost all of the humpback strandings that have occurred in New York and New Jersey this winter had clear signs of vessel strike, though it is unknown if the collisions occurred before or after the whales died. (Most of the full necropsy results are still pending.)
Even before the pandemic, vessel strikes and gear entanglement were among the main causes of anthropogenic mortality among large whales globally, and among North Atlantic humpbacks in particular. The species has been called “cosmopolitan” for its ability to seemingly tolerate the urbanized waters of the New York Bight. A study published in 2021 found that humpbacks foraging in the nearshore waters of this region between 2018 and 2020 “were exclusively juveniles that were surface feeding,” and that 93 percent of humpbacks struck were juveniles.
“I don’t want to say there are only juveniles in the New York Bight,” says Lesley Thorne, a co-author of the 2021 study and an associate professor in Stony Brook University’s School of Marine and Atmospheric Sciences. “But certainly” — compared to adults — “they are the animals occurring close to shore and [are] potentially more vulnerable because of that difference in habitat use.” Thorne says scientists are not yet sure why juveniles are more prevalent closer to shore, though Robbins pointed out that young humpbacks seem to chase Atlantic menhaden more than adults do.
In 2008, NOAA established speed restrictions to help reduce the risk of vessel strikes for large whales, particularly North Atlantic right whales. But the rule is difficult to enforce, especially as shipping channels become more crowded with more ships and whales. “We’ve been documenting vessel strikes and entanglements in large whales for decades, but it’s also becoming more prevalent as vessels get faster and fishing rope gets stronger,” says Michael Moore, a senior scientist at the Woods Hole Oceanographic Institute who has spent his 40-plus-year career studying marine mammals, with a focus on North Atlantic right whales. “So the tools for trauma are there, and they’re well defined in terms of what is causing mortality. At what point does an unusual event become usual?”
Not only are vessels crowding the water’s surface, where humpbacks feed. They are also making it loud down below. The New York Bight’s submarine environment is constantly subjected to sounds from shipping and other sources, including the pinging of sonar from government activities, which may include nautical charting and geologic mapping; from academic institutions conducting historical geological studies; and from beach replenishment operations searching for suitable sand deposits.
“We’re fighting this battle against Cousteau’s silent world,” says an ocean researcher. “It’s not quiet down there.”
“We’re fighting this battle against Cousteau’s silent world,” says Doug Nowacek, who heads the Nowacek Acoustics and Engineering Lab at Duke University, which is currently researching how sound from the development of offshore wind sites might impact marine mammals. “It’s not quiet down there.”
Understanding this level of din is important when trying to asses the impact of other sources of sound — like the seafloor surveys conducted by Ørsted and Atlantic Shores — on whales such as humpbacks. The companies have used several types of survey equipment that use high frequency sound waves to map the seafloor within their lease areas. High frequency sounds are harder for baleen whales to hear, Nowacek says, and have not been shown to impact them beyond behavioral disturbances. Additionally, says Nowacek, these high frequency pulses quickly lose intensity as they spread from their target area on the seafloor.
The types of sounds that baleen whales are most sensitive to are low frequency and meant to travel long distances. The most well-known uses of low frequency sound are military sonar and seismic surveying conducted by the oil and gas industry, which uses huge arrays equipped with dozens of air guns to pulse sound waves kilometers below the seafloor. Both Ørsted and Atlantic Shores did conduct surveys that utilize lower frequencies, but because they only need to penetrate about 100 feet into the seafloor, the equipment is much smaller and emits far less sound-intensive pulses. (While military sonar has been directly linked to baleen whale strandings, seismic surveying has not.)
According to an Ørsted spokesperson, the company has not conducted those tests “offshore of South Jersey since the summer of 2022.” It is unclear when Atlantic Shores last used lower frequency surveying. Nevertheless, for a humpback to be disoriented enough by Ørsted’s surveying — even its lowest frequency activity — “it would have to be basically right next to it,” says Nowacek. Such a close encounter is unlikely, given that all offshore wind survey ships are required to have trained observers onboard whose job is to ensure that marine mammals are avoided and that sonar work is stopped when they are nearby.
Nowacek stressed that the impact of noise on marine mammals “is not something to be trifled with.” He and other scientists also emphasize that they are concerned by how little is still known about how the North Atlantic is changing, how marine mammal behavior might shift as a result of those changes, and how hundreds of wind turbines in the marine environment might further exacerbate all this change.
“We’re trying to understand why these whales are here, to look at the resources they’re depending on,” says Robbins, of the Center for Coastal Studies. “There’s whole teams of people working under really terrible conditions, conducting necropsies, trying to look at each death carefully.” The questions are challenging, she adds, and they continue to mount. “But to draw a conclusion before a very complicated question has been sorted out is actually just drawing resources and attention away from the thing it might really be.”